Celestial Navigation · Sextant Corrections
When the lower limb of the Sun is brought to the horizon, the semi-diameter correction is:
- ASubtracted
- BAdded✓ Correct
- CApplied only to stars
- DEqual to the dip
Explanation
Because the Almanac tabulates the center of the Sun but the navigator sights a limb, a semi-diameter correction is applied: add SD for a lower-limb sight, subtract SD for an upper-limb sight. Stars and planets are treated as points (negligible SD).
Authority: Nautical Almanac
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